Laura Peeters

The trunk in spinal musclar atrophy | 101 5 Joint torque Trunk joint torques were significant lesser (p<0.01) for patients with SMA compared to HC in all directions, with median values slightly below 50% of HC (Table 2). Median shoulder torques were below 25% of HC in patients with SMA. SMA type 2 patients seemed weaker compared to type 3 patients, although the numbers were too small for statistical testing. Active range of motion tasks The numbers of participants with missing values in trunk ROM and muscle activity outcomes are shown in Table 3. Maximum active trunk angles were significantly lower (p<0.01) in all directions in patients with SMA compared to HC (Figure 2A). Median trunk flexion angle was reduced the most, approximately by 58°, followed by axial rotation (36°), extension (27°) and lateral bending (24°). There was no significant difference between lateral bending and axial rotation to the dominant or non-dominant side. Normalized muscle activity levels when flexing and extending were not different between patients with SMA and HC for the muscles primarily counteracting gravitational moments (e.g. back muscles for trunk flexion, abdominal muscles for trunk extension) (Figure 2B). However, there was a significant increase (p<0.01) in normalized antagonistic activation for patients with SMA, i.e. the abdominal muscles for flexion (up to 29% MVIC), back muscles for extension (up to 24% MVIC) and ipsilateral back muscles for lateral bending (up to 39% MVIC). Normalized muscle activity of the ipsilateral back and abdominal muscles were also significantly greater (p<0.05) for axial rotation (up to 24% MVIC) in patients with SMA. Healthy controls SMA n median IQR n median IQR P-value HC/ SMA Trunk (flexion) 15 54.4[47.8-70.7] 13 23.7 [20.7-34.4] 0.001 Trunk (extension) 15 59.6[46.8-84.3] 13 25.9 [11.2-47.7] 0.001 Trunk (lateral bending D) 15 66.4[52.7-86.9] 13 29.2 [17.7-42.8] 0.005 Trunk (lateral bending ND) 15 63.1[47.5-75.0] 13 31.6 [16.2-42.7] 0.004 Shoulder abduction (D) 15 47.9[35.4-57.0] 16 11.3 [5.1-17.4] <0.001 Shoulder abduction (ND) 15 42.1[31.0-54.5] 14 9.8 [4.9-13.0] <0.001 Table 2 Maximum trunk joint torque (in Nm) in four directions. Abbreviations: D = towards dominant side; ND = towards non-dominant side